Control of selective catalytic reduction (SCR) catalysts is of increasing interest to meet modern internal combustion engine emissions standards. The effectiveness of a typical SCR catalyst in removing oxides of nitrogen (NOx) emissions is sensitive to the temperature of the exhaust gas at the inlet to the SCR catalyst. Current catalyst formulations typically operate at optimal efficiency when subjected to exhaust gas temperatures of 200-400° C. and utilize ammonia over the SCR catalyst to reduce NOx. However, engine operating conditions often occur in which the SCR catalyst is operating outside of optimal efficiency temperature conditions.
Reductant consumption in aftertreatment system operations is an operating cost that must be incurred by owners and operators of the engine. When SCR catalysts operate at high temperatures, the parasitic oxidation of ammonia to N2, N2O, or NOx can occur depending on the reaction over the catalyst and the operating conditions. The oxidation conversion amount increases as the exhaust temperature increases, which requires the injection of additional reductant to compensate for the oxidized ammonia and increases operating costs. Improvements in aftertreatment system design and control are required to reduce and optimize reductant consumption. Accordingly, further technological developments in this area are desirable.